PET/CT – the most precise cancer diagnostics method
Meet LILITA ROZNERE, Radiologist/Therapist at the "RSU Nuclear Medicine Clinic" and the Oncology Centre of Latvia.
Is it true that PET/CT is such a unique method – the most accurate for cancer diagnostics? I have read about the study carried out in the USA that 24 000 patients were diagnosed cancer by using classical methods – ultrasound, computed tomography, biopsy – and straight after they were tested using the positron emission tomography (PET/CT) which resulted in radical changes in the treatment of around 36% of the patients?
It is a remarkable indicator and actually implies that without the PET/CT examination almost 9 thousand patients would have received improper treatment. I have been working in the area of oncology for 15 years and as an attending physician I have often had the necessity for PET/CT examination, but for many years it was not available to us. We felt miserable; the method was available in the neighbouring countries – for a long time in Tallinn, in two State-owned clinics in Lithuania, Russia, all over the Europe – and Latvia was the only one without PET/CT! I felt sorry for my patients, because the number of patients with oncological diagnoses is considerable. Therefore, I am very happy that we have the opportunity to offer PET/CT examinations here in Latvia.
What are the advantages of a PET/CT examination?
The main difference is that PET/CT is a combined imagining tool which allows perform two different examinations at once – computed tomography (CT) and positron emission tomography (PET), providing three informative scan images. The first is a CT image, reflecting human body's anatomical structure – it allows to take a look at organs, measure them and determine dimensions of formations. The second is a PET image – a functional image precisely displaying any malignant cells, their behaviour as well as physiological processes. These two images are digitally combined – the anatomical image is merged with the functional image and the third, the so-called hybrid image is obtained which is of the uppermost importance and provides comprehensive information about the tumour.
When a patient already knows that he/she has cancer – has already underwent ultrasound or computed tomography examination and the cancer has been shown in biopsy –PET/CT examination is an important step for establishing whether the illness has not spread all over the body and to determine the precise stage of it. PET/CT is a wholebody examination which allows the attending physician to take a strategical decision on the required further treatment much faster.
What do you mean by the spread of illness, do you mean metastasis?
Not only that. For example, PET/CT scan is frequently applied also by haematologists who deal with malignant illnesses of blood and haematogenous organs – lymphomas and leucosis, since these tumours are primarily systemic disorders and not a single focus disease as, for example, breast cancer. If the specialists know which lymphatic tissues contain cancer cells it is much easier to choose the most appropriate treatment method.
Why do cancer cells beam during the examination?
Before launching the PET examination, a special radiopharmaceutical is administered to the patient by intravenous injection that distributes evenly across the body and sends a signal to the diagnostics device. In order to precisely detect and transmit information on the cancer cells, the radiopharmaceutical is mixed with glucose, which accumulates in the cells consuming sugar most effectively. Basing upon the results of the examination we see the consumption of glucose by human tissues – muscles, viscera that is reflected as certain glowing. Malignant tumours stand out particularly – they constantly grow using sugar for energy, therefore, during the examination they intake glucose more intensively. During a PET/CT scan we are able to see tumours as glowing spots on the overall background. Thus, the malignant tumours reveal their location, size and other important information.
Can the treatment vary substantially if precise spread of the illness is not known?
Of course! An example – a woman is diagnosed breast cancer. If the surgeon or the attending physician knows the particular focus, it can be removed; however, if the specialist discovers that the woman does not only have the primary cancer, but the disease has spread to bones, lymphatic glands and other organs, a completely different therapy would be required instead.
Another important aspect of the PET/CT examination is to determine the treatment efficiency. For example, at the very beginning of the treatment six to nine cycles of chemotherapy are prescribed. The PET/CT examination is used in the middle of the therapy, for example, after three cycles of chemotherapy, and in case we can see that there are no functionally active tumour tissues in the patient's body – nothing is glowing during the examination, the tumour has been stopped! Conclusion!? The rest chemotherapy cycles are no longer required. Thus, first of all, the patient's body is not poisoned with chemicals. And second, this saves resources, since chemotherapy is rather expensive. The method allows to detect improper treatment for a certain form of cancer and change the applied medicine in due time.
The third case when the use of PET/CT examination is advisable and valuable – at the end of the treatment of an oncological patient. The patient has undergone surgery, chemotherapy, radiation therapy and after a year or earlier a PET/CT scan should be the best method for reassuring that everything is all right and the tumour has not resurrected.
I would like to emphasize that PET/CT by no means cancels other examinations. For example, ultrasound and mammography of mammary glands or ultrasound of gynaecologic organs, lung x-ray, etc. Various examinations supplement each other.
What should be done if the cancer does not glow?
All patients are checked before the procedure, whether the particular type of cancer can be examined by this method. We would not examine a patient, if we knew that the PET/CT method is not suitable in the particular case. Taking into account metabolic processes of the human body various radiopharmaceutical preparations have been created that allow accessing specific types of cancer. For example, a malignant tumour of prostate consumes no glucose at all, therefore in case of the prostate cancer the examination is carried out by applying other preparations – choline (18F-Choline) or gallium (68Ga-PSMA). 68Ga-PSMA has been globally recognised as the most efficient preparation for diagnostics of the prostate cancer – it is prostate-specific membrane antigen, a highly sensitive agent that does not attach to any other inflammation processes with the exception of the androgen receptor in prostate cancer cells. This method allows detecting the prostate cancer, assessing the cancer spread and differentiates between inflammation processes and tumours. Gallium imaging is especially crucial for recurrence of cancer after the previous surgery or radiation therapy. It provides precise and early diagnosis of recurrence already at the PSA levels below 1.0. Studies show that gallium may detect metastases smaller than 5 mm in the lymph nodes. Such finding can substantially change the pace of treatment.
PET/CT examination of prostate is very important as it immediately shows whether pelvic lymph nodes are already malignant and if lymph nodes should be removed during surgery. However, in case the surgeon is not aware of such malignancy, he removes solely the prostate gland, whereby lymph nodes remain untouched and the tumour continues spreading. Besides, the largest lymph node is not always malignant; at times a small lymph node can contain malignant cells and can be left where it is. It is important to know that.
What is the size of metastases that can be detected by PET/CT?
According to the literature – from up to 9 millimetres. But in practice we can see smaller ones. A lymph node of 4 millimetres in size, but it glows! We measure the intensity of radiation accumulation, which is an objective parameter, and it shows that the node intensively consumes glucose. It is clear that the node is malignant.
What is your greatest professional contentment during these months while you work with the new equipment?
Our first patient, whom we examined using PET/CT had a lymphoma. He had undergone the treatment and we had to determine whether the treatment is complete or it has to be continued. We scanned him and he was, as we say, clean. We were very happy to bring such great news over to him.
On the same day, we examined a young woman, who underwent the treatment of haematological tumour. Because of the applied therapy, she had various complications, she had bravely got through that, but the computed tomography still showed suspicious focal points in her abdominal cavity. Her lymph nodes were enlarged; they decreased in the course of therapy, yet did not disappear. Having undergone a PET/CT examination we established that the focal points are metabolically inactive. Thus, there were only tissues of tumour, but the disease was no longer viable. We had the pleasure to give good news to this patient as well.
But there is also the other side – we are those who tell the news worse than the patient has hoped and the doctor expected. The attending physician is aware of one focal point, but we find another three-four, even more. Unfortunately… So, there are good news and bad news, but both are valuable, because the information acquired in the course of the examination is a fact that the attending physician can work with, for example, change the treatment method.
Are there situations when PET/CT is not needed? A person wants and can afford it – but there is no need to.
There are people who suffer from cancerophobia or simply increased concern about their health, and they are ready to invest money and undergo examinations, although they have no indications for a PET/CT examination. We commonly persuade these individuals that no examination is needed and suggest them to consult a doctor. A PET/CT examination needs a purpose – a doctor who refers a patient to the examination asks specific questions to the radiologist-diagnostician in order to decide on further treatment of the patient – whether it is therapy control or he is interested in the spread or relapse of the disease.
How to apply for the PET/CT examination?
The PET/CT examinations at the Diagnostics Centre "Nuclear Medicine Clinic" are carried out on the basis of the presented prescription – it can be issued by a general practitioner, oncologist, surgical oncologist, haematologist, urologist or another specialist who is of the opinion that the patient needs a PET/CT examination (indications for PET/CT examination). It is also possible to arrange a visit with the in-house oncologist at "Nuclear Medicine Clinic", who will carry out scrupulous examination of your health condition, medical history, advise on the necessary examinations and further treatment and, if necessary, order a PET/CT examination.